The investigated area of the Koreničko Vrelo spring catchment area is situated in the Lika district, in central Croatia. This is part of the well-known Dinaric karst region, characterized by a strike of geological structures NW-SE, deep karstification as a consequence of compression of structures, and reverse faulting. Triassic, Jurassic and Cretaceous rocks, predominantly limestones and dolomites, show high tectonic disturbance and destruction ; they are karstified and partially covered with Quaternary deposits. The Koreničko Vrelo (Fig. 1) is capped for the water supply of the small town of Korenica and adjacent villages. It is a typical karst spring with a marked difference in discharge quantity from the minimum (a few tens of l/s) to the maximum (above 1 m3). It is part of a wider hydrogeological system represented by karst springs: Korenička Rijeka, Mlinac, Kameniti Vrelac, Stipinovac and Koreničko Vrelo, besides a few springs of lesser importance. From the Korenička rijeka spring begins a stream (small river) called Matica. The stream is situated in the middle of a valley covered with Quaternary deposits, and the above-mentioned karst springs are situated on the right (western) side of the Matica. The majority of the rocks that form their catchment area and aquifer are composed of karstified limestones. All these springs appear at almost the same elevation of about 700 m a.s.l., a fact connected with the regional fault in whose zone the springs occur. On this fault, limestones from the hinterland are in contact with dolomites under quaternary deposits in the valley. On the eastern side of the Matica there is small dolomitic hill, with many springs of low discharge on its flank. Since the Korničko Vrelo is situated within an inhabited area, there is a high danger of micro-biological pollution. Therefore it is important to remove the water extraction site outside the village, and to reach the groundwater in the karst underground by boreholes before it wells out. Bulk hydrogeological investigations have been performed for that purpose, and are still continuing. Up to now, structural geological analysis of the terrain has been performed, as well as detailed hydrogeological mapping, hydrochemical research, prospecting of 27 springs in the area, geophysical explorations, core drillings, and monitoring of water quality and quantity (Andrić et al., 2006 ; Pavičić et al., 2006). The whole investigated area is situated inside the boundaries of the well-known "Plitvička jezera" national park. That circumstance is very important, because every kind of research procedure needs to be conducted with minimal impact on the environment. That particularly applies to bore-hole drilling. Although the Koreničko vrelo catchment area has no direct hydrological impact on the Plitvička jezera lakes, it is important to protect that part of the National park environment as well, and that includes groundwater use. Special permission needs to be obtained from the Croatian Ministry of Culture and the National Park management. Every exploratory procedure or step needs to be conducted with the knowledge of the park rangers who have the task of monitoring them.